3-dimensional printing

ABSTRACT

The present disclosure is drawn to coalescent inks and material sets for 3D printing. The coalescent ink can include a water-soluble near-infrared dye having a peak absorption wavelength from 800 nm to 1400 nm. The coalescent ink can also contain water.

BACKGROUND

Methods of 3-dimensional (3D) digital printing, a type of additivemanufacturing, have continued to be developed over the last few decades.

However, systems for 3D printing have historically been very expensive,though those expenses have been coming down to more affordable levelsrecently. In general, 3D printing technology improves the productdevelopment cycle by allowing rapid creation of prototype models forreviewing and testing. Unfortunately, the concept has been somewhatlimited with respect to commercial production capabilities because therange of materials used in 3D printing is likewise limited.Nevertheless, several commercial sectors such as aviation and themedical industry have benefitted from the ability to rapidly prototypeand customize parts for customers.

Various methods for 3D printing have been developed, includingheat-assisted extrusion, selective laser sintering, photolithography, aswell as others. In selective laser sintering, a powder bed is exposed topoint heat from a laser to melt the powder wherever the object is to beformed. This method is very slow and can take more than eight hours toproduce a simple part. The resulting part also lacks edge accuracy andsmoothness. Additionally, this method does not produce colored objectsvery easily. It has also been an expensive method, with the system costtypically exceeding $200,000. Accordingly, development of new 3Dprinting technologies continues.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates absorption spectrum for a tertiary amine watersoluble near-infrared dye in accordance with examples of the presentdisclosure;

FIG. 2 illustrates an absorption spectrum for a tetraphenyldiamine watersoluble near-infrared dye in accordance with examples of the presentdisclosure;

FIG. 3 illustrates an absorption spectrum for a tetraphenyldiamine watersoluble near-infrared dye in accordance with examples of the presentdisclosure; and

FIG. 4 is a flowchart illustrating a method for forming a 3D printedpart in accordance with examples of the present disclosure.

DETAILED DESCRIPTION

The present disclosure is drawn to the area of 3D printing. Morespecifically, the present disclosure provides near-infrared coalescentinks and material sets for printing 3D parts.

In light area processing (LAP), a thin layer of polymer powder is spreadon a bed to form a powder bed. A printing head, such as an inkjet printhead, is then used to print a coalescent ink over portions of the powderbed corresponding to a thin layer of the three dimensional object to beformed. Then the bed is exposed to a light source, e.g., typically theentire bed. The coalescent ink absorbs more energy from the light thanthe unprinted powder. The absorbed light energy is converted to thermalenergy, causing the printed portions of the powder to melt and coalesce.This forms a solid layer. After the first layer is formed, a new thinlayer of polymer powder is spread over the powder bed and the process isrepeated to form additional layers until a complete 3D part is printed.In accordance with the present technology, this LAP process can achievefast throughput with good accuracy.

To absorb and convert the light energy to thermal energy, near-infrareddyes can be used in the coalescent inks. These near-infrared dyes canabsorb light wavelengths in the range of about 800 nm to 1400 nm andconvert the absorbed light energy to thermal energy. When used with alight source that emits a wavelength in this range and a polymer powderthat has a low absorbance in this range, the near-infrared dye causesthe printed portions of the polymer powder to melt and coalesce withoutmelting the remaining polymer powder. Thus, near-infrared dyes can bejust as efficient or even more efficient at generating heat andcoalescing the polymer powder when compared to carbon black (which isalso effective at absorbing light energy and heating up the printedportions of the powder bed, but has the disadvantage of always providingblack or gray parts in color).

According to the present technology, coalescent inks can be formulatedwith near-infrared dyes so that the near-infrared dye has substantiallyno impact on the apparent color of the ink. This allows the formulationof colorless coalescent inks that can be used to coalesce the polymerpowder but which will not impart noticeably visible color to the polymerpowder. Alternatively, the coalescent inks can include additionalpigments and/or dyes to give the inks a color such as cyan, magenta,yellow, blue, green, orange, violet, black, etc. Such colored coalescentinks can be used to print colored 3D parts with acceptable opticaldensity. The coalescent inks can also be formulated with near-infrareddyes that are stable in the ink vehicle and that provide good inkjetting performance. The near-infrared dyes can also be compatible withthe polymer powder so that jetting the ink onto the polymer powderprovides adequate coverage and interfiltration of the dyes into thepowder.

The near-infrared dye can therefore be selected based on its absorptionspectrum, its solubility in the ink vehicle, and its compatibility withthe polymer powder. FIGS. 1-3 show absorption spectra for threedifferent near-infrared dyes. FIG. 1 is the absorption spectrum for atertiary amine near-infrared dye and FIGS. 2-3 are absorption spectrafor two different tetraphenyldiamine near-infrared dyes. Each of thesedyes has very low absorbance in the visible light range, which is about400 nm to 700 nm. However, each dye has a very high absorbance in therange of 800 nm to 1400 nm.

The near-infrared dye is of course not limited to the dyes illustratedin the figures or the dyes listed above. Other dyes can also besuitable. In one example, the coalescent ink can include a water-solublenear-infrared dye having a peak absorption wavelength from 800 nm to1400 nm, wherein the near infrared dye is selected from the groupconsisting of aminium dyes, tetraaryldiamine dyes, cyanine dyes,dithiolene dyes, and combinations thereof. The coalescent ink can alsoinclude a colorant, e.g., a pigment that imparts a visible color to thecoalescent ink and water.

In some examples, the concentration of near-infrared dye in thecoalescent ink can be from 0.1 wt % to 25 wt %. In one example, theconcentration of near-infrared dye in the coalescent ink can be from 0.1wt % to 15 wt %. In another example, the concentration can be from 0.1wt % to 10 wt %. In yet another example, the concentration can be from0.5 wt % to 5 wt %.

The concentration can be adjusted to provide a coalescent ink in whichthe visible color of the coalescent ink is not substantially altered bythe near-infrared dye. Although near-infrared dyes generally have verylow absorbance in the visible light range, the absorbance is usuallygreater than zero. Therefore, the near-infrared dyes can typicallyabsorb some visible light, but their color in the visible spectrum isminimal enough that it does not substantially impact the inks ability totake on another color when a colorant is added (unlike carbon blackwhich dominates the inks color with gray or black tones). The pure dyesin powder form can have a visible color, such as light green, lightbrown or other colors depending on the absorption spectrum of thespecific dye. Concentrated solutions of the dyes can also have a visiblecolor. Accordingly, the concentration of the near-infrared dye in thecoalescent ink can be adjusted so that the dye is not present in such ahigh amount that it alters the visible color of the coalescent ink. Forexample, a near-infrared dye with a very low absorbance of visible lightwavelengths can be included in greater concentrations compared to anear-infrared dye with a relatively higher absorbance of visible light.These concentrations can be adjusted based on a specific applicationwith some experimentation.

In further examples, the concentration of the near-infrared dye can behigh enough that the near-infrared dye impacts the color of thecoalescent ink, but low enough that when the ink is printed on a polymerpowder, the near-infrared dye does not impact the color of the polymerpowder. The concentration of the near-infrared dye can be balanced withthe amount of coalescent ink that is to be printed on the polymer powderso that the total amount of dye that is printed onto the polymer powderis low enough that the visible color of the polymer powder is notimpacted. In one example, the near-infrared dye can have a concentrationin the coalescent ink such that after the coalescent ink is printed ontothe polymer powder, the amount of near-infrared dye in the polymerpowder is from 0.1 wt % to 1.5 wt % with respect to the weight of thepolymer powder.

The near-infrared dye can have a temperature boosting capacitysufficient to increase the temperature of the polymer powder above themelting or softening point of the polymer powder. As used herein,“temperature boosting capacity” refers to the ability of a near-infrareddye to convert near-infrared light energy into thermal energy toincrease the temperature of the printed polymer powder over and abovethe temperature of the unprinted portion of the polymer powder.Typically, the polymer powder particles can be fused together when thetemperature increases to the melting or softening temperature of thepolymer. As used herein, “melting point” refers to the temperature atwhich a polymer transitions from a crystalline phase to a pliable,amorphous phase. Some polymers do not have a melting point, but ratherhave a range of temperatures over which the polymers soften. This rangecan be segregated into a lower softening range, a middle softening rangeand an upper softening range. In the lower and middle softening ranges,the particles can coalesce to form a part while the remaining polymerpowder remains loose. If the upper softening range is used, the wholepowder bed can become a cake. The “softening point,” as used herein,refers to the temperature at which the polymer particles coalesce whilethe remaining powder remains separate and loose. When the coalescent inkis printed on a portion of the polymer powder, the near-infrared dye canheat the printed portion to a temperature at or above the melting orsoftening point, while the unprinted portions of the polymer powderremain below the melting or softening point. This allows the formationof a solid 3D printed part, while the loose powder can be easilyseparated from the finished printed part.

Although melting point and softening point are often described herein asthe temperatures for coalescing the polymer powder, in some cases thepolymer particles can coalesce or be sintered together at temperaturesslightly below the melting point or softening point. Therefore, as usedherein “melting point” and “softening point” can include temperaturesslightly lower, such as up to about 20° C. lower, than the actualmelting point or softening point.

In one example, the near-infrared dye can have a temperature boostingcapacity from about 10° C. to about 30° C. for a polymer with a meltingor softening point from about 100° C. to about 350° C. If the powder bedis at a temperature within about 10° C. to about 30° C. of the meltingor softening point, then such a near-infrared dye can boost thetemperature of the printed powder up to the melting or softening point,while the unprinted powder remains at a lower temperature. In someexamples, the powder bed can be preheated to a temperature from about10° C. to about 30° C. lower than the melting or softening point of thepolymer. The coalescent ink can then be printed onto the powder and thepowder bed can be irradiated with a near-infrared light to coalesce theprinted portion of the powder.

The coalescent ink can also include a pigment or dye colorant thatimparts a visible color to the coalescent ink. In some examples, thecolorant can be present in an amount from 0.5 wt % to 10 wt % in thecoalescent ink. In one example, the colorant can be present in an amountfrom 1 wt % to 5 wt %. In another example, the colorant can be presentin an amount from 5 wt % to 10 wt %. However, the colorant is optionaland in some examples the coalescent ink can include no additionalcolorant. These coalescent inks can be used to print 3D parts thatretain the natural color of the polymer powder. Additionally, coalescentink can include a white pigment such as titanium dioxide that can alsoimpart a white color to the final printed part. Other inorganic pigmentssuch as alumina or zinc oxide can also be used.

In some examples, the colorant can be a dye. The dye may be nonionic,cationic, anionic, or a mixture of nonionic, cationic, and/or anionicdyes. Specific examples of dyes that may be used include, but are notlimited to, Sulforhodamine B, Acid Blue 113, Acid Blue 29, Acid Red 4,Rose Bengal, Acid Yellow 17, Acid Yellow 29, Acid Yellow 42, AcridineYellow G, Acid Yellow 23, Acid Blue 9, Nitro Blue Tetrazolium ChlorideMonohydrate or Nitro BT, Rhodamine 6G, Rhodamine 123, Rhodamine B,Rhodamine B Isocyanate, Safranine O, Azure B, and Azure B Eosinate,which are available from Sigma-Aldrich Chemical Company (St. Louis,Mo.). Examples of anionic, water-soluble dyes include, but are notlimited to, Direct Yellow 132, Direct Blue 199, Magenta 377 (availablefrom Ilford AG, Switzerland), alone or together with Acid Red 52.Examples of water-insoluble dyes include azo, xanthene, methine,polymethine, and anthraquinone dyes. Specific examples ofwater-insoluble dyes include Orasol® Blue GN, Orasol® Pink, and Orasol®Yellow dyes available from Ciba-Geigy Corp. Black dyes may include, butare not limited to, Direct Black 154, Direct Black 168, Fast Black 2,Direct Black 171, Direct Black 19, Acid Black 1, Acid Black 191, MobayBlack SP, and Acid Black 2.

In other examples, the colorant can be a pigment. The pigment can beself-dispersed with a polymer, oligomer, or small molecule; or can bedisperses with a separate dispersant. Suitable pigments include, but arenot limited to, the following pigments available from BASF: Paliogen®)Orange, Heliogen® Blue L 6901F, Heliogen®) Blue NBD 7010, Heliogen® BlueK 7090, Heliogen® Blue L 7101F, Paliogen®) Blue L 6470, Heliogen®) GreenK 8683, and Heliogen® Green L 9140. The following black pigments areavailable from Cabot: Monarch® 1400, Monarch® 1300, Monarch®) 1100,Monarch® 1000, Monarch®) 900, Monarch® 880, Monarch® 800, and Monarch®)700. The following pigments are available from CIBA: Chromophtal®)Yellow 3G, Chromophtal®) Yellow GR, Chromophtal®) Yellow 8G, Igrazin®Yellow 5GT, Igralite® Rubine 4BL, Monastral® Magenta, Monastral®Scarlet, Monastral® Violet R, Monastral® Red B, and Monastral® VioletMaroon B. The following pigments are available from Degussa: Printex® U,Printex® V, Printex® 140U, Printex® 140V, Color Black FW 200, ColorBlack FW 2, Color Black FW 2V, Color Black FW 1, Color Black FW 18,Color Black S 160, Color Black S 170, Special Black 6, Special Black 5,Special Black 4A, and Special Black 4. The following pigment isavailable from DuPont: Tipure®) R-101. The following pigments areavailable from Heubach: Dalamar® Yellow YT-858-D and Heucophthal Blue GXBT-583D. The following pigments are available from Clariant: PermanentYellow GR, Permanent Yellow G, Permanent Yellow DHG, Permanent YellowNCG-71, Permanent Yellow GG, Hansa Yellow RA, Hansa Brilliant Yellow5GX-02, Hansa Yellow-X, Novoperm® Yellow HR, Novoperm® Yellow FGL, HansaBrilliant Yellow 10GX, Permanent Yellow G3R-01, Hostaperm® Yellow H4G,Hostaperm® Yellow H3G, Hostaperm® Orange GR, Hostaperm® Scarlet GO, andPermanent Rubine F6B. The following pigments are available from Mobay:Quindo® Magenta, Indofast® Brilliant Scarlet, Quindo® Red R6700, Quindo®Red R6713, and Indofast® Violet. The following pigments are availablefrom Sun Chemical: L74-1357 Yellow, L75-1331 Yellow, and L75-2577Yellow. The following pigments are available from Columbian: Raven®7000, Raven® 5750, Raven® 5250, Raven® 5000, and Raven® 3500. Thefollowing pigment is available from Sun Chemical: LHD9303 Black. Anyother pigment and/or dye can be used that is useful in modifying thecolor of the coalescent in and/or ultimately, the printed part.

The colorant can be included in the coalescent ink to impart color tothe printed object when the coalescent ink is jetted onto the powderbed. Optionally, a set of differently colored coalescent inks can beused to print multiple colors. For example, a set of coalescent inksincluding any combination of cyan, magenta, yellow (and/or any othercolors), colorless, white, and/or black coalescent inks can be used toprint objects in full color. Alternatively or additionally, a colorlesscoalescent ink can be used in conjunction with a set of colored,non-coalescent inks to impart color. In some examples, a colorlesscoalescent ink containing a near-infrared dye can be used to coalescethe polymer powder and a separate set of colored or black or white inksnot containing the near-infrared dye can be used to impart color.

The components of the coalescent ink can be selected to give the inkgood ink jetting performance and the ability to color the polymer powderwith good optical density. Besides the near-infrared dye and thecolorant, if present, the coalescent ink can include a liquid vehicle.Liquid vehicle formulations that can be used with the organic-solublenear-infrared dyes described herein can include water and one or moreco-solvents present in total at from 1 wt % to 50 wt %, depending on thejetting architecture. Further, one or more non-ionic, cationic, and/oranionic surfactant can optionally be present, ranging from 0.01 wt % to20 wt %. In one example, the surfactant can be present in an amount from5 wt % to 20 wt %. The liquid vehicle can also include dispersants in anamount from 5 wt % to 20 wt %. The balance of the formulation can bepurified water, or other vehicle components such as biocides, viscositymodifiers, materials for pH adjustment, sequestering agents,preservatives, and the like. In one example, the liquid vehicle can bepredominantly water. Because the near-infrared dyes are soluble inwater, an organic co-solvent is not necessary to solubilize thenear-infrared dye. Therefore, in some examples the coalescing ink can besubstantially free of organic solvent. However, in other examples aco-solvent can be used to help disperse other dyes or pigments, orimprove the jetting properties of the ink.

Classes of co-solvents that can be used can include organic co-solventsincluding aliphatic alcohols, aromatic alcohols, diols, glycol ethers,polyglycol ethers, caprolactams, formamides, acetamides, and long chainalcohols. Examples of such compounds include primary aliphatic alcohols,secondary aliphatic alcohols, 1,2-alcohols, 1,3-alcohols, 1,5-alcohols,ethylene glycol alkyl ethers, propylene glycol alkyl ethers, higherhomologs (C₆-C₁₂) of polyethylene glycol alkyl ethers, N-alkylcaprolactams, unsubstituted caprolactams, both substituted andunsubstituted formamides, both substituted and unsubstituted acetamides,and the like. Specific examples of solvents that can be used include,but are not limited to, 2-pyrrolidinone, N-methylpyrrolidone,2-hydroxyethyl-2-pyrrolidone, 2-methyl-1,3-propanediol, tetraethyleneglycol, 1,6-hexanediol, 1,5-hexanediol and 1,5-pentanediol.

One or more surfactants can also be used, such as alkyl polyethyleneoxides, alkyl phenyl polyethylene oxides, polyethylene oxide blockcopolymers, acetylenic polyethylene oxides, polyethylene oxide(di)esters, polyethylene oxide amines, protonated polyethylene oxideamines, protonated polyethylene oxide amides, dimethicone copolyols,substituted amine oxides, and the like. The amount of surfactant addedto the formulation of this disclosure may range from 0.01 wt % to 20 wt%. Suitable surfactants can include, but are not limited to, liponicesters such as Tergitol™ 15-S-12, Tergitol™ 15-S-7 available from DowChemical Company, LEG-1 and LEG-7; Triton™ X-100; Triton™ X-405available from Dow Chemical Company ; and sodium dodecylsulfate.

Consistent with the formulation of this disclosure, various otheradditives can be employed to optimize the properties of the inkcomposition for specific applications. Examples of these additives arethose added to inhibit the growth of harmful microorganisms. Theseadditives may be biocides, fungicides, and other microbial agents, whichare routinely used in ink formulations. Examples of suitable microbialagents include, but are not limited to, NUOSEPT® (Nudex, Inc.),UCARCIDE™ (Union carbide Corp.), VANCIDE® (R. T. Vanderbilt Co.),PROXEL® (ICI America), and combinations thereof.

Sequestering agents, such as EDTA (ethylene diamine tetra acetic acid),may be included to eliminate the deleterious effects of heavy metalimpurities, and buffer solutions may be used to control the pH of theink. From 0.01 wt % to 2 wt %, for example, can be used. Viscositymodifiers and buffers may also be present, as well as other additives tomodify properties of the ink as desired. Such additives can be presentat from 0.01 wt % to 20 wt %.

In one example, the liquid vehicle can include the components andamounts as shown in Table 1:

TABLE 1 Ingredients Wt (%) 2-Pyrrolidinone 50-752-Methyl-1,3-Propanediol  5-12 Tetraethylene glycol  5-12 LEG-1  5-10Surfynol ® CT151 surfactant from Air Products and 0.2-1.2 Chemicals,Inc. Zonyl ® FSO fluorosurfactant from DuPont 0.01-1   SMA1440H 1-5 Trisbase 0.1-1 

In another example, the liquid vehicle can include the components andamounts as shown in Table 2:

TABLE 2 Ink Components Wt (%) 2-Pyrrolidinone 50-100 Crodafos N3 ™surfactant from Croda 0.1-5  

In yet another example, the liquid vehicle can include the componentsand amounts as shown in Table 3:

TABLE 3 Component Wt. % 2-methyl-1,3-propanediol  10-40 Crodafos N3 ™surfactant from Croda 0.1-5 Tergitol ™ 15-S-12 surfactant from DowChemical Company 0.1-3 Zonyl ® FSO-100 fluorosurfactant from DuPont0.5-5 Proxel ™ GXL (20% as is) biocide from Lonza 0.1-1

In still another example, the liquid vehicle can include the componentsand amounts as shown in Table 4:

TABLE 4 Component Wt. % 2-Hydroxyethyl-2-Pyrrolidone 5-20 Dantocol ™ DHEbonding agent from Lonza 30-80  LEG 1-20 Crodafos N3 ™ surfactant fromCroda 1-20 Surfynol ® SEF (75% as is) surfactant from Air 1-10 Productsand Chemicals, Inc. Kordek ™ MLX (10% as is) biocide from 0.1-5   DowChemical Company Proxel ™ GXL (20% as is) biocide from Lonza 0.1-5  

In a further example, the liquid vehicle can include the components andamounts as shown in Table 5:

TABLE 5 Ink vehicle components Wt. % Tripropylene glycol 20-601-(2-Hydroxyethyl)-2-imidazolidinone 20-40 LEG-1 0.5-5  Crodafos N3 ™surfactant from Croda 1-6 Tergitol ™ 15-S-7 surfactant from 1-6 DowChemical Company Zonyl ® FSO fluorosurfactant from DuPont 0.1-1.2Proxel ™ GXL biocide from Lonza 0.1-1.2

It is noted the liquid vehicle formulations of Tables 1 to 5 areprovided by example only and other formulations with similar propertiescan likewise be formulated in accordance with the present technology.

The present technology also includes material sets for 3D powder bedprinting. A material set for 3D powder bed printing can include acoalescent ink containing a water-soluble near-infrared dye having apeak absorption wavelength from 800 nm to 1400 nm and water. Thematerial set can also include a particulate polymer formulated tocoalesce when contacted by the coalescent ink and irradiated by anear-infrared energy emitting the peak absorption wavelength. Thecoalescent ink can include any of the components described herein.

The particulate polymer can be a polymer powder. In one example, thepolymer powder can have an average particle size from 10 to 100 microns.The particles can have a variety of shapes, such as substantiallyspherical particles or irregularly-shaped particles. In some examples,the polymer powder can be capable of being formed into 3D printed partswith a resolution of 10 to 100 microns. As used herein, “resolution”refers to the size of the smallest feature that can be formed on a 3Dprinted part. The polymer powder can form layers from about 10 to about100 microns thick, allowing the coalesced layers of the printed part tohave roughly the same thickness. This can provide a resolution in thez-axis direction of about 10 to about 100 microns. The polymer powdercan also have a sufficiently small particle size and sufficientlyregular particle shape to provide about 10 to about 100 micronresolution along the x-axis and y-axis.

In some examples, the particulate polymer can be colorless. For example,the particulate polymer can have a white, translucent, or transparentappearance. In combination with a coalescing ink having an invisiblenear-infrared dye and no additional colorant, this can provide a printedpart that is white, translucent, or transparent. In other examples, theparticulate polymer can be colored for producing colored parts. In stillother examples, when the polymer powder is white, translucent, ortransparent, color can be imparted to the part by the coalescent ink orother ink, as previously described.

The particulate polymer can have a melting or softening point from about100° C. to about 350° C. In further examples, the polymer can have amelting or softening point from about 150° C. to about 200° C. A varietyof thermoplastic polymers with melting points or softening points inthese ranges can be used. For example, the particulate polymer can beselected from the group consisting of nylon 6 powder, nylon 9 powder,nylon 11 powder, nylon 12 powder, nylon 66 powder, nylon 612 powder,polyethylene powder, thermoplastic polyurethane powder, polypropylenepowder, polyester powder, polycarbonate powder, polyether ketone powder,polyacrylate powder, polystyrene powder, and mixtures thereof. In aspecific example, the particulate polymer can be nylon 12, which canhave a melting point from about 175° C. to about 200° C. In anotherspecific example, the particulate polymer can be thermoplasticpolyurethane.

The particulate polymer and the near-infrared dye used in the coalescentink can be selected to have compatible properties. For example, thenear-infrared dye, when printed on a portion of the particulate polymer,can have a sufficient temperature boosting capacity so that the printedportion of the particulate polymer increases in temperature by at least10° C. more than a non-printed portion of the particulate polymer whenboth the printed portion and the non-printed portion are irradiated witha wavelength of about 800 nm to about 1400 nm.

In some examples, the water-soluble near-infrared dye can be present inthe coalescent ink at a relatively low concentration, so that thenear-infrared dye is molecularly dispersed when the coalescent ink isprinted onto the particulate polymer. The dye molecules caninterfiltrate into the particulate polymer and passivate surfaces of thepolymer particles. In one example, the liquid vehicle of the coalescentink can evaporate after the ink is printed onto the polymer particles.This leaves behind the near-infrared dye molecules and other pigmentsand dyes, if present, on the surfaces of the polymer particles. Becausecoalescence of the polymer particles depends strongly on melting orsoftening of the surfaces of the particles, the dye molecules at thesurfaces can provide efficient coalescence of the particles. Because thedye molecules are water-soluble, the dye molecules can easily be removedfrom the surface of the finished part by washing the part with water.

FIG. 4 is a flowchart of a method 400 for forming a 3D printed part. Themethod includes preheating a bed of particulate polymer to about 10° C.to about 30° C. below a melting point or softening point of theparticulate polymer 410; jetting a coalescent ink onto a portion of thebed of particulate polymer, wherein the coalescent ink comprises awater-soluble near-infrared dye having a peak absorption wavelengthbetween 800 nm and 1400 nm and water 420; irradiating the bed ofparticulate polymer with a fusing lamp configured to emit a wavelengthfrom 800 nm to 1400 nm to cause the portion of the bed of particulatepolymer to fuse 430; adding a layer of particulate polymer to theportion after fusing 440; and repeating the jetting, irradiating, andadding steps to form a part 450.

In one example, the bed of particulate polymer can be formed byintroducing polymer powder from a polymer powder supply and rolling thepowder in a thin layer using a roller. The coalescent ink can be jettedusing a conventional ink jet print head, such as a thermal ink jet (TIJ)printing system. The amount of coalescent ink printed can be calibratedbased on the concentration of near-infrared dye in the ink, thetemperature boosting capacity of the near-infrared dye, among otherfactors. The amount of coalescent dye printed can be sufficient tocontact near-infrared dye with the entire layer of polymer powder. Forexample, if each layer of polymer powder is 100 microns thick, then thecoalescent ink can penetrate at least 100 microns into the polymerpowder. Thus the near-infrared dye can heat the polymer powderthroughout the entire layer so that the layer can coalesce and bond tothe layer below. After forming a solid layer, a new layer of loosepowder can be formed, either by lowering the powder bed or by raised theheight of the roller and rolling a new layer of powder.

The entire powder bed can be preheated to a temperature below themelting or softening point of the polymer powder. In one example, thepreheat temperature can be from about 10° C. to about 30° C. below themelting or softening point. In another example, the preheat temperaturecan be within 50° C. of the melting of softening point. In a particularexample, the preheat temperature can be from about 160° C. to about 170°C. and the polymer powder can be nylon 12 powder. In another example,the preheat temperature can be about 90° C. to about 100° C. and thepolymer powder can be thermoplastic polyurethane. Preheating can beaccomplished with one or more lamps, an oven, a heated support bed, orother types of heaters. In some examples, the entire powder bed can beheated to a substantially uniform temperature.

The powder bed can be irradiated with a fusing lamp configured to emit awavelength from 800 nm to 1400 nm. Suitable fusing lamps can includecommercially available infrared lamps and halogen lamps. The fusing lampcan be a stationary lamp or a moving lamp. For example, the lamp can bemounted on a track to move horizontally across the powder bed. Such afusing lamp can make multiple passes over the bed depending on theamount of exposure needed to coalesce each printed layer. The fusinglamp can be configured to irradiate the entire powder bed with asubstantially uniform amount of energy. This can selectively coalescethe printed portions with near-infrared absorbing dyes while leaving theunprinted portions of the polymer powder below the melting or softeningpoint.

In one example, the fusing lamp can be matched with the near-infrareddye so that the fusing lamp emits wavelengths of light that match thehighest absorption wavelengths of the dye. A dye with a narrow peak at aparticular near-infrared wavelength can be used with a fusing lamp thatemits a narrow range of wavelengths at approximately the peak wavelengthof the dye.

Similarly, a dye that absorbs a broad range of near-infrared wavelengthscan be used with a fusing lamp that emits a broad range of wavelengths.Matching the dye and the fusing lamp in this way can increase theefficiency of coalescing the polymer particles with the dye printedthereon, while the unprinted polymer particles do not absorb as muchlight and remain at a lower temperature.

Depending on the amount of near-infrared dye present in the polymerpowder, the absorbance of the near-infrared dye, the preheattemperature, and the melting or softening point of the polymer, anappropriate amount of irradiation can be supplied from the fusing lamp.In some examples, the fusing lamp can irradiate each layer from about0.5 to about 10 seconds.

In some cases, modifying inks can be used to address thermal bleed so asto improve the surface quality of the final printed part. The modifyinginks can include materials having low thermal conductivity such aspotassium iodide, sodium iodide or potassium sulfate. The modifying inkscan be printed at boundaries between coalescing portions andnon-coalescing portions, to slow heat dissipation from the coalescingportions to neighboring polymer particles. This can improve separationbetween the fused and unfused areas of the powder bed.

It is to be understood that this disclosure is not limited to theparticular process steps and materials disclosed herein because suchprocess steps and materials may vary somewhat. It is also to beunderstood that the terminology used herein is used for the purpose ofdescribing particular examples only. The terms are not intended to belimiting because the scope of the present disclosure is intended to belimited only by the appended claims and equivalents thereof.

It is noted that, as used in this specification and the appended claims,the singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise.

As used herein, “liquid vehicle” or “ink vehicle” refers to a liquidfluid in which colorant is placed to form an ink. A wide variety of inkvehicles may be used with the systems and methods of the presentdisclosure. Such ink vehicles may include a mixture of a variety ofdifferent agents, including, surfactants, solvents, co-solvents,anti-kogation agents, buffers, biocides, sequestering agents, viscositymodifiers, surface-active agents, water, etc. Though not part of theliquid vehicle per se, in addition to the colorants and/or water-solublenear-infrared dyes, the liquid vehicle can carry solid additives such aspolymers, latexes, UV curable materials, plasticizers, salts, etc.

As used herein, “colorant” can include dyes and/or pigments.

As used herein, “dye” refers to compounds or molecules that absorbelectromagnetic radiation or certain wavelengths thereof. Dyes canimpart a visible color to an ink if the dyes absorb wavelengths in thevisible spectrum. Additionally, “near-infrared dye” refers to a dye thatabsorbs primarily in the near-infrared region of the spectrum, i.e.,about 800 nm to about 1400 nm.

As used herein, “pigment” generally includes pigment colorants, magneticparticles, aluminas, silicas, and/or other ceramics, organo-metallics orother opaque particles, whether or not such particulates impart color.Thus, though the present description primarily exemplifies the use ofpigment colorants, the term “pigment” can be used more generally todescribe not only pigment colorants, but other pigments such asorganometallics, ferrites, ceramics, etc. In one specific aspect,however, the pigment is a pigment colorant.

As used herein, “soluble,” when referring to a dye, refers to the dyehaving a solubility percentage of more than 5 wt %.

As used herein, “ink-jetting” or “jetting” refers to compositions thatare ejected from jetting architecture, such as ink-jet architecture.Ink-jet architecture can include thermal or piezo architecture.Additionally, such architecture can be configured to print varying dropsizes such as less than 10 picoliters, less than 20 picoliters, lessthan 30 picoliters, less than 40 picoliters, less than 50 picoliters,etc.

As used herein, the term “substantial” or “substantially” when used inreference to a quantity or amount of a material, or a specificcharacteristic thereof, refers to an amount that is sufficient toprovide an effect that the material or characteristic was intended toprovide. The exact degree of deviation allowable may in some casesdepend on the specific context.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint. The degree offlexibility of this term can be dictated by the particular variable anddetermined based on the associated description herein.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to includeindividual numerical values or sub-ranges encompassed within that rangeas if each numerical value and sub-range is explicitly recited. As anillustration, a numerical range of “about 1 wt % to about 5 wt %” shouldbe interpreted to include not only the explicitly recited values ofabout 1 wt % to about 5 wt %, but also include individual values andsub-ranges within the indicated range. Thus, included in this numericalrange are individual values such as 2, 3.5, and 4 and sub-ranges such asfrom 1-3, from 2-4, and from 3-5, etc. This same principle applies toranges reciting only one numerical value. Furthermore, such aninterpretation should apply regardless of the breadth of the range orthe characteristics being described.

EXAMPLES

The following illustrates several examples of the present disclosure.

However, it is to be understood that the following are only illustrativeof the application of the principles of the present disclosure. Numerousmodifications and alternative compositions, methods, and systems may bedevised without departing from the spirit and scope of the presentdisclosure. The appended claims are intended to cover such modificationsand arrangements.

Example 1

A tertiary amine-based water soluble near-infrared dye (FHI 98811S fromFabricolor Holding International) and two tetraphenyldiamine-based watersoluble near-infrared dyes (FHI 994312S and FHI 104422P from FabricolorHolding International) were obtained. The absorption spectra of thesedyes in water are illustrated in FIGS. 1-3. The dyes have absorptionswithin the range of 800 to 1400 nm and which fall within the emissivespectrum of an infrared lamp used in the LAP process. The infrared lampemits radiation corresponding to blackbody radiation at a temperature of2200° C. The infrared lamp has a λ_(max) wavelength of about 1100 nm andquickly forms a tail end at higher wavelengths. Dyes with a similarabsorption range can efficiently convert energy from the infrared lampinto thermal energy. Of the tested dyes, the absorption range of FHI104422P matches the range of the infrared lamp most closely. Initialexperiments were carried out by making ink dispersions with FHI 104422P.First, aqueous solutions of the dye were made with two differentconcentrations of dye. Then an ink vehicle consisting of components suchas 2-pyrrolidinone, 2-methyl-1,3-propanediol, tetraethylene glycol,liponic ester, surfynol CT151, Zonyl FSO and tris base was prepared. Theink vehicle was mixed with the aqueous dye solutions so that the inkvehicle was present in an amount of 30 wt % in each of the final inksolutions. The overall content of dye in the final ink solutions was 1wt % in the first ink solution and 2.5 wt % in the second ink solution.For each ink, a 100 micron layer of thermoplastic polyurethane (TPU)powder was heated to 90° C. and then the ink was printed to form ashape. The powder was then exposed to the infrared lamp. This raised thetemperature, causing the printed TPU particles to fuse. Another layer of100 micron thickness of TPU powder was coated over the bed and theprocess was repeated to obtain the final part. The final part wasretrieved from the build bed and cleaned by mild sand blasting. Thefinal part obtained with 1 wt % dye in the ink adopts the natural colorof the TPU. When the dye concentration is increased to 2.5 wt %, thecolor is slightly darker. Both parts had good color consistency.Increasing the concentration of dye to 2.5 wt % in the ink increases thefusing efficiency of the TPU particles but also darkens the final colorslightly. Further optimization can yield good mechanical properties.Post annealing of the part can also increase the mechanical propertieswithout altering the accuracy of the part. The same process was repeatedwith FHI 98811S and FHI 994312S. The ink prepared with FHI 98811S hadprintability issues with kogation whereas FHI 994312S yielded similarresults to FHI 104422P.

Example 2

FHI 104422P (0.75 g) was dissolved in water (51.75 g). An ink vehiclewas prepared according to the ratio of chemicals in Table 6. Inaddition, additives such as Crodafos, PEI, glycerol or glycolic acidesters and ethers and or SDS surfactant can be added. This ink vehicle(22.5 g) is added to the above dye solution to make an ink containing 1wt % of the near-infrared dye. A similar process is followed to make inkwith 2.5 wt % of the dye in the ink. The mechanical properties of thefinal part can be further adjusted by post annealing the sample to 150°C. and cooling to ambient temperature.

TABLE 6 Ink Components Wt % 2-Pyrrolidinone 75 2-Methyl-1,3-Propanediol7 Tetraethylene glycol 7 LEG-1 6.36 Surfynol ® CT151 surfactant from Air0.99 Products and Chemicals, Inc. Zonyl ® FSO fluorosurfactant from 0.09DuPont SMA1440H 3.11 Tris base 0.45

Example 3

Example 2 is repeated under similar conditions except using the inkvehicle (22.5 g) from Table 7.

TABLE 7 Ink Components Wt % 2-Pyrrolidinone 98.7 Crodafos N3 ™surfactant 1.6 from Croda

Example 4

Example 2 is repeated under similar conditions except using the inkvehicle (22.5 g) from Table 8.

TABLE 8 Ink Components Wt % 2-methyl-1,3-propanediol 95.9 Crodafos N3 ™surfactant from Croda 1.3 Tergitol ™ 15-S-12 surfactant from 1.3 DowChemical Company Zonyl ® FSO-100 fluorosurfactant from 1 DuPont Proxel ™GXL (20% as is) biocide from 0.5 Lonza

Example 5

Example 2 is repeated under similar conditions except using the inkvehicle (22.5 g) from Table 9.

TABLE 9 Ink Components Wt % 2-Hydroxyethyl-2-Pyrrolidone 20.3 Dantocol ™DHE bonding agent 67.7 from Lonza LEG 2.0 Crodafos N3 ™ surfactant fromCroda 2.0 Surfynol ® SEF surfactant from Air 6.8 Products and Chemicals,Inc. Kordek ™ MLX biocide from 0.6 Dow Chemical Company Proxel ™ GXLbiocide from Lonza 0.6

Example 6

Example 2 is repeated under similar conditions except using the inkvehicle (22.5 g) from Table 10.

TABLE 10 Ink components Wt % Tripropylene glycol 52.51-(2-Hydroxyethyl)-2-imidazolidinone 40 LEG-1 2 Crodafos N3 ™ surfactantfrom Croda 2 Tergitol ™ 15-S-7 surfactant from 2 Dow Chemical CompanyZonyl ® FSO fluorosurfactant from DuPont 1 Proxel ™ GXL biocide fromLonza 0.5

Example 7

TPU powder was heated to 90° C. in a test bed. Then the ink is printedin the desired location to make a test shape. Uniform temperature ismaintained in the test bed. The infrared lamp is then swept across theentire test bed area to fuse the particles in the ink printed area. Anadditional layer of powder is next spread on the test bed and theprocess continued to form a complete test part. The part is taken out ofthe powder bed and mildly sand blasted. Tests part prepared using inkswith 1 wt % dye are nearly colorless. Test parts prepared using inkswith 2.5 wt % dye have a light green color. Each test part has thecharacteristic flexibility of polyurethane. Each test part also has goodcolor uniformity.

Example 8

An ink is prepared by the same method as in Example 2, but with FHI994312S dye instead of FHI 104422P. The same printing process describedin Example 7 is used to form test parts and similar results areobtained.

Example 9

The inks of Examples 2 to 6 are prepared to have a specific desiredcolor by adding a colorant to the inks (in addition to the near-infrareddye, which is essentially colorless or imparts only a pale color). Inthis example, to each of these inks, 1 wt %, 2 wt %, 3.5 wt %, 5 wt %,or 7 wt % of any one of a cyan, magenta, yellow, or black pigment (selfdispersed or dispersant dispersed) is added to the inks by replacing anequivalent amount of one or more of the major solvents, e.g., water,2-pyrrolidinone, 2-methyl-1,3-propanediol,2-hydroxyethyl-2-pyrrolidinone, etc., or an equivalent amount of theliquid vehicle as a whole.

What is claimed is:
 1. A coalescent ink for 3-dimensionoal printing,comprising: a water-soluble near-infrared dye having a peak absorptionwavelength from 800 nm to 1400 nm, wherein the near-infrared dye isselected from the group consisting of aminium dyes, tetraaryldiaminedyes, cyanine dyes, dithiolene dyes, and combinations thereof; acolorant imparting a visible color to the coalescent ink; and water. 2.The coalescent ink of claim 1, wherein the near-infrared dye does notsubstantially alter the visible color of the coalescent ink.
 3. Thecoalescent ink of claim 1, wherein the near-infrared dye has atemperature boosting capacity of about 10° C. to about 30° C. for apolymer with a melting point of about 100° C. to about 350° C.
 4. Thecoalescent ink of claim 1, further wherein the colorant is a pigment. 5.The coalescent ink of claim 1, wherein the near-infrared dye has aconcentration of 0.1 wt % to 25 wt % in the coalescent ink.
 6. Thecoalescent ink of claim 1, wherein the pigment has a concentration of0.5 wt % to 10 wt % in the coalescent ink.
 7. The coalescent ink ofclaim 1, wherein the coalescent ink imparts a visible color when jettedonto polymer particles and provides a concentration of near-infrared dyeof 0.1 wt % to 1.5 wt % with respect to the polymer particles.
 8. Amaterial set for 3-dimensional powder bed printing, comprising: acoalescent ink comprising water and a water-soluble near-infrared dyehaving a peak absorption wavelength from 800 nm to 1400 nm; and aparticulate polymer formulated to coalesce when contacted by thecoalescent ink and irradiated by a near-infrared energy emitting thepeak absorption wavelength.
 9. The material set of claim 8, wherein thenear-infrared dye is selected from the group consisting of aminium dyes,tetraaryldiamine dyes, cyanine dyes, dithiolene dyes, and combinationsthereof.
 10. The material set of claim 8, wherein the coalescent inkfurther comprises a pigment imparting a visible color to the coalescentink.
 11. The material set of claim 8, wherein the particulate polymer isselected from the group consisting of nylon 6 powder, nylon 9 powder,nylon 11 powder, nylon 12 powder, nylon 66 powder, nylon 612 powder,polyethylene powder, thermoplastic polyurethane powder, polypropylenepowder, polyester powder, polycarbonate powder, polyether ketone powder,polyacrylate powder, polystyrene powder, and mixtures thereof.
 12. Thematerial set of claim 8, wherein the particulate polymer has a meltingor softening point from about 100° C. to about 350° C.
 13. The materialset of claim 8, wherein the near-infrared dye, when printed on a portionof the particulate polymer, has a sufficient temperature boostingcapacity so that the printed portion of the particulate polymerincreases in temperature by at least 10° C. more than a non-printedportion of particulate polymer when both the printed portion and thenon-printed portion are irradiated with a wavelength of about 800 nm toabout 1400 nm.
 14. A method for forming a 3-dimensional printed part,comprising: preheating a bed of particulate polymer to about 10° C. toabout 30° C. below a melting point or softening point of the particulatepolymer; jetting a coalescent ink onto a portion of the bed ofparticulate polymer, wherein the coalescent ink comprises: awater-soluble near-infrared dye having a peak absorption wavelengthbetween 800 nm and 1400 nm, and water; irradiating the bed ofparticulate polymer with a fusing lamp configured to emit a wavelengthfrom 800 nm to 1400 nm to cause the portion of the bed of particulatepolymer to fuse; adding a layer of particulate polymer to the portionafter fusing; and repeating the jetting, irradiating, and adding stepsto form a part.
 15. The method of claim 14, wherein the fusing lamp isconfigured to expose the entire bed of particulate polymer to asubstantially uniform irradiation intensity.